METHODS OP MANUFACTURE. 213'.
aind it is of ten impossible on a series of heats, as" the wearing bf the hearth or the accumulation of slag will give a gain or a Ipss. In Table :XII-0 the term "'first slag" signifies "that which flows through', the.port opening, and is thus removed from the furnace during the progress of the operation-, while "second slag" means the cinder from the furnace at the time of tapping. ' :. . ;i /;;,;.
Taking as a basis the weight of pig-iron and recarburizer, the, weight of ingots and scrap together was* 103.1 per cent, in the case of the cold metal,. and 104.95- per cent, with liquid metal., These figures neglect entirely the weight of ore charged, but'it is* customary, to speak, of such practice by saying that the gains were. 3.1 per cent, and 4.95 per cent, respectively. This subject will, be again referred to in other sections ,of this chapter.
In the case of the cold pig, the first and second slags together carried away 7.3 per cent, of all the-metallic iron put into the furnace, including! the .iron in the ore. In. the case of the melted iron, this loss was 7.4 per cent. The silicon in the pig-iron was 1.4 per cent., which is high for basic practice. Had it, been lower there would have been less, silica produced', Iqss lime would have been necessary, less slag would have been produced, and less, iron-would have been lost in the cinder. T'hejslag is npt exactly proportionate to, .the silicon in the iron, as there are other sources from which siHca is supplied, but had the silicon in.the .pig-iron- been reduced one-half, to a content, of 0.70 per- cent., the -volume- of slag'would; have been only two-thirds as much, and it would-carry away less* than ,5: per cent., of the total iron in the charge, which would mean;; a gadn: of 2.5 per .cent, in .the-weight- of ingots -over the- actual' prJEic-tice.and. give. a. total gain in.weight of 7.5 per cent. Less ore would-be required with lower silicon, but on the other-hand, a- lower percentage of silicon means a, higher content of metallic' iron in the*1 pig-iron, which is bound to show itself in a greater product.
SEC. XIIc.-T-27/te Talbeit process.The last section described the-difficulties encountered in the use of the-pig-and-ore process in a. furnace-that cannot be tilted while in operation. -A way; of' overmanning this trouble has been carried out by Mr. Talbot.* A-, tilting', furnace is used, and when the charge is ready to tap,-a1 portion of': the steel, and a portion only; is poured into the ladle-and cast'int'o ' ingots. The remainder is fcfept in the furnace- and .a new. supply of.
i ' '* Journal I ana.S. I,, Vpl. 1,1900.. ...... ,. .'